Amateur Position (or Packet) Reporting System

This mode of operation was developed in 1984 as an off-shoot of amateur radio
packet data systems and GPS (Global Positioning System, or Sat Nav). It was invented by an American
radio amateur called Bob Bruninga, callsign WB4APR.

The basis of APRS is almost any amateur radio transmitter, plus a GPS
receiver and a PC. The GPS receiver knows where it is, with
an accuracy of perhaps 50 feet, or even 6 feet. The APRS can send this
information to others. Every now and then, the system wakes up, transmits a
quick burst of data, then goes back to sleep. Essentially, it is saying
only "This is who I am and this is where I am". For short range,
APRS may be used on the VHF or UHF bands. For long range, it may be used
on the HF bands.

This data burst of about 0.3 seconds contains only the callsign of the transmitting
person and his map reference. It makes it all
simple and quick. People receiving direct or repeated APRS data bursts can
use a computer to display the callsign and location of an APRS station on a
screen map. The progress of a vehicle or a walker can be seen as an icon
on the map.

Facilities and Hardware

To use APRS at a fixed location, the hardware required is minimal: a
transceiver, a PC and a couple of cables joining them together. A GPS
receiver is not really required as the location won't change.

The PC generates and decodes the data tones. Its APRS program displays
stations on a map and has the facility to track a moving station i.e. it
automatically changes maps as the station reaches the edge of a map.

The system has more facilities. A short text comment can be
inserted into the data burst e.g. "It is snowing and the temp is -42
degrees". Like the position information, the message is sent at
intervals in "unconnected mode", meaning that the sender doesn't know
who (if anybody) receives it.

A PC is required to display the locations of APRS stations and it can be used
in a building or a vehicle. There are situations in which the reception of
APRS is unimportant, but the sending of APRS information is the main point.
RAYNET operators on key vehicles and with key personnel on foot can use a mobile
or hand portable transceiver with a small APRS tracker box and GPS receiver.

Another facility is the sending of short text messages which are acknowledged
i.e. the sender knows that they were received. The minimum APRS data burst
with callsign and location is about 0.3 seconds. When a short text message
is added, the data burst is about 1 second. APRS stations using a simple
tracker box can't receive such messages but can send fixed broadcast messages.

Digital Repeaters

Although un-manned amateur radio fixed location speech repeaters require
special amateur radio licences, any amateur radio station can act as a repeater
for data modes. Such a repeater of digital information is called a
digipeater, or digi for short.

People on foot with low power hand portable transceivers sending APRS signals
(tracker beacons) won't have much of a range on VHF or UHF. As nearby
mobile stations and fixed stations in buildings will act as digipeaters,
everybody in a given area receives all other tracker beacons.

In addition to the ad hoc digipeater system, many areas of the UK have
well-sited unattended VHF digipeaters which are specially licensed.

More out of this world is the fact that the ISS (International Space Station)
has a digipeater which receives and relays APRS data signals. Many of the
astronauts are also radio amateurs. See more details by clicking this
link.

Beacon Timing

The time interval between transmitting location beacons is typically every 30
minutes for a fixed station. This also applies to a car which is parked.

The timing for a mobile or walking APRS station depends on the
circumstances. The user programs his equipment for best results. It
could be one location beacon every 3 minutes or every 1 km or every 1
mile. The shortest interval is every 6 seconds but that wouldn't be much
use for most events and would waste radio channel time.

APRS via the Internet

In general, the UK amateur radio licence allows any licensed person to
connect amateur radio transmissions to the Internet. It does NOT allow a
connection FROM the Internet TO amateur radio bands. It is a one way
system.

Any radio amateurs with the interest in APRS can connect their
computers to the internet and pass received APRS signals to a website. In this way, anybody can
access the relevant internet pages and see where APRS stations are, or where
they were last seen at
which time. Their broadcast messages can also be seen.

In addition, many areas of the UK have enthusiasts who obtain a special
licence to run a permanent APRS Internet Gateway (I Gate) station. This
allows them to operate in both directions i.e. they can receive APRS signals
from the Internet and transmit them onto amateur radio bands.

The ad hoc digipeater system, whereby any APRS station can also act as a
digipeater, plus the 24 hour well-sited fixed digipeaters and the IGate stations
altogether form an enormous international radio network.

You can park your car in the centre of a large city and may expect a direct
range on VHF of only a few miles due to the proximity of large buildings. If you
are in range of a single station which is part of the APRS network, another
radio amateur in Greece, Australia or the USA can see you as an icon on a map
and can type short messages to you.

This may sadden some of the older radio amateurs, as they don't consider it
to be real amateur radio if Internet wires are used to join stations together.

Local IGate Stations

Keith in Springwell, Gateshead, Tyne & Wear, owns MB7UXX. It may be
out of range to Teesside stations. IGate station MB7UVU in Witton-le-Wear
covers Teesside.

RAYNET Use of APRS

What purposes can the facilities of automatic location pinpointing and short
typed messages serve and where can they be used? An APRS
transmitter can be in a building (they don't tend to move much), in a vehicle,
on a river boat, hand held on foot or at sea on a ship. Amateur radio
transmitters are forbidden to be used on any aircraft, although RAYNET did do
this on helicopters during the Lockerbie PanAm flight 103 disaster, with special
permission from the UK licensing authority.

When Bob Bruninga invented APRS in 1984, his first practical use of the mode
was at a public service event, supporting a 100 mile horse endurance ride.
He and friends passed messages giving the location and status of the horses.

Yorkshire RAYNET Groups provided admin and emergency communications on 20 May
2007 for the Etape du Dales event. This was a 110 mile cycle ride on
public roads in the counties of North Yorkshire and Cumbria with 715
cyclists. As well as manning strategic check points on the route, RAYNET
operators provided APRS in four ambulances, two support vehicles and the chase
car. The RAYNET Control station in the village of Grassington could see
with a glance at a PC, the location of all seven key vehicles.

Similarly, APRS could be employed on other events which
take place over a large area and over an extended period, at which it is useful
to have an instant map readout of the locations of certain people. The map
could be available on the screen of a RAYNET PC or via internet access to many
organisations.

APRS could also be used for monitoring things such as flood levels at a
prolonged incident. There could be widespread flooding across a
county. Local authority Emergency Planning Officers and police may welcome
information about flood levels at many places, to co-ordinate local government
facilities to deal with a changing situation. The PC map could show RAYNET
callsign, location and water level. Graphs could be drawn by software,
showing the changing water levels at many locations.

Sample APRS Map

Click the thumbnail sized picture below to see a larger version.
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Icons and Tactical Callsigns

The icon to be displayed on the map is selected by the sender. It could
be a house for a fixed station. It could also be a car, jeep, lorry, space
shuttle, speedboat, walker, fire engine, police car, ambulance or many other
icons.

For most amateur radio use, the icon will show the amateur radio callsign of
the sender. For RAYNET use, it could show a tactical callsign of up to 6
characters. If this is done, the licence rules say that the true callsign
must be included in the comment or message part of the beacon.